Market for Web App Idea

I have a web application in mind and I'd like to know if there is a market for it. I will need a report stating whether or not this software would be a viable product that can make money, supported by facts, links , details. By "web application" I mean software that is installed on a webspace. Examples of which are: - phpBB - phpNuke - Mediawiki My specific idea will involve Quickbooks-like features. More information provided by PM upon request. Samples of previous work *must* be provided and it must be high quality, since I intend to invest in the idea based upon what you report. (Budget for the project is up to $150, but you'll have to justify the extra cost to me).